Caps for cervix uteri as a birth control means have been known for a long time and have been found among the artifacts of antiquity. It has been reported that Aetius of Amida suggested for this purpose the use of a pomegranate shell cut into a hollow cup, and that beeswax discs fashioned to fit over the cervix have been used in Europe.
Modern cervical caps comprise a pre-formed rubber cap that is positioned over the cervix uteri to act as a sperm barrier. Such caps are manufactured in several sizes to accommodate the various uterine sizes normally encountered; however, with such caps the fit for a particular individual is inexact and necessarily a compromise. As a result, these caps often become dislodged during coitus and have to be removed periodically to accommodate normal uterine discharges. Thus, such caps are inconvenient to use and have not achieved a high degree of reliability.
Typifying the many types of cervical caps that have been developed are those shown in U.S. Pat. Nos. 2,836,177 to Sells, 3,952,737 to Lipfert et al and 4,007,249 to Erb, German Pat. No. 475,496 to Leopold, as well as in Das Weibliche Gebar-Unvermogen by F. A. Wilde in Berlin in 1838 according to aforementioned U.S. Pat. No. 4,007,249. These cervical caps have met with varying degrees of success. In particular, the cap shown in U.S. Pat. No. 4,007,249 to Erb is said to be made while the vaginal wall is expanded by means of a speculum. Such an expedient tends to deform the cervix and thus precludes a good fit between the cap and the cervix because the attendant cervical distortion exceeds the limits of prosthetic stability of the produced cap. Additionally, medical grade silicone rubber, the material of choice in said patent for making the cap, is not readily wettable, thus surface tension cannot be relied upon to hold the cap properly in place on the cervix. In addition, some medical grade silicone rubbers are porous, and mucous uterine discharges and bacteria are likely to accummulate in the pores, thereby causing unpleasant odor, in addition to a risk of infection. In such instances, cervical caps may be usable only for a limited time period, e.g., about 6-8 hours.
The foregoing expedient is also impractical because the surface to which the liquid, polymerizable material is applied is wet with mucus and quite slippery, thus the applied material is likely to fall off the exocervical surface due to gravity before polymerization of the material could take place and, in any event, it would be impossible to control the thickness of the applied polymerizable material during in situ polymerization. A cervical cap having a relatively non-uniform thickness is undesirable, however, because it is unstable and is likely to be dislodged in use.
A further shortcoming of the caps shown in the Erb patent is that the prefabricated valving means utilized are of the leaflet or flap type. In such valves a viscous droplet of cervical mucus can hold the valve in an open position for an undesirably long time period, thereby providing an access aperture for sperm and defeating the very purpose of the cap. Moreover, inasmuch as the polymerizable material of the cap is in a fluid state when it surrounds the prefabricated valve, some of the fluid material may become enmeshed with the valve and interfere with its intended valving action after the material has polymerized.
U.S. Pat. No. 4,007,249 to Erb also briefly mentions a technique disclosed initially by F. A. Wilde in 1838 in Das Weibliche-Gebar-Unvermogen according to which a cervical cap allegedly can be made from a special wax impression of the vaginal portion of the cervix. As recognized by Erb, such a technique cannot produce an identical, negative-image, cervix-conforming inside surface because the cervix would be deformed while the wax impression is being made. The uterus is suspended in the lower abdomen by ligaments, is easily movable, and would tend to move up into the abdomen even with a gentle force applied to the cervix. As a result, accurate registration would be prevented by such a movement with attendant lack of stability for the cervical cap produced in such manner.
The techniques described by Erb are also likely to suffer from the same drawback, albeit for a different reason. In particular, in practicing these techniques the vaginal wall has to be expanded using a vaginal speculum or similar implement in order to expose the cervix during cap molding. This expedient tends to distort the cervix as well, elongating it along an imaginary line between the tips of the inserted, open vaginal speculum blades and shortening the cervix along an imaginary line at right angles to the imaginary line between the tips of the speculum blades. The attendant cervical distortion exceeds the limits for prosthetic stability of the cervical cap that is produced.